It fluctuates a lot. The base is down to about 3,000 books now but it was recently double that.
I have been doing a lot of "soul searching" and have decided to narrow the collection down to about 1,000 books which would include only the runs of stuff I really care about.
That would leave me with mainly keys and a full run of X-Men up to issue 300 something.
I still haven't decided if I want to get rid of my full runs of Spawn and Silver Surfer Vol. 3. Neither is really worth anything or ever will be, but those are two of the core collections that really drove me into everything else I have gotten into. Spawn is still on going and I plan to keep buying them (recently got much better).
So, I am rambling but part of me wants to really purge and get down to just the basics. It is really hard getting rid of anything, but the more I get rid of stuff the more I start thinking I should continue to purge!